The present invention relates to measuring temperature in electrical machines using fiber optics and, more particularly, to monitoring winding temperatures by interrogation of reflections from a series of laser pulses injected into an optical fiber routed along an armature winding.
Current practice makes use of resistive temperature detectors (RTD's) to measure armature temperature. This provides local temperature information only at the location of the RTD and only at the outer surface of the armature bar or coil. Information about the actual copper temperature can be obtained only with thermocouples embedded in the copper strands. This requires that thermocouples be routed through the ground wall insulation, and this method is therefore applied only for special test purposes and rarely in production machines.
Location of hot spot is currently obtained by locating multiple RTD's in a stator slot along the stack length. This provides approximate information about the hot spot in the stator slot, but provides no information about winding temperature in the stator end windings.
Temperature measurement using fiber optics has been performed successfully in buried cables, but not with sufficient resolution to be useful for temperature monitoring of generator or motor windings. Other methods based on optical gratings placed at discreet locations have been shown to provide finer spatial resolution in aerospace applications. It would be desirable to find a way to make this principle work in the electrical winding in electrical machines, such as turbomachinery, hydrogenerators or electric motors, without compromising machine integrity.